Made available in DSpace on 2015-05-14T12:14:04Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 2407959 bytes, checksum: db27c0e32c73a0b37eaa484bdc506772 (MD5) Previous issue date: 2009-01-22 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The approach of this thesis is study the laser emission from highly scattering media with gain with incoherent feedback. These systems are called of random lasers and diverge from the typical laser, because they can emit monochrome light with high intensity without a cavity. We detail several experimental studies in samples containing different rhodamines in solution containing TiO2 nanoparticles, which provide the feedback to lasing. The nanoparticles densities were chosen for random laser system remains in a diffusive regime. In this regime, the probability of the photon return to the starting point of incidence is unlikely; therefore the interference effects of waves associated to the photons can be neglected and the feedback is incoherent. We study de dependence of random laser threshold on both dye concentration C and scatterers density N. We showed that the dependence of random laser threshold on the nanoparticles density is a power law N-α, but the exponent α depends on the dye concentration. We used the novel random laser spectroscopy technique to study de binding energy between molecules in the dimers, our results agree very well with those found by other authors who used traditional methods. We also showed, by the first time, the random laser emission from aqueous solution containing rhodamines 6G and TiO2 nanoparticles, Sodium Dodecyl Sulfate (SDS) was added to dissolve the dye aggregates. / A emissão de luz tipo laser a partir de meios altamente espalhadores com ganho com realimentação incoerente é a abordagem desta tese. Estes meios são altamente desordenados e divergem do conceito tradicional do laser convencional, pois eles podem emitir luz muito intensa e monocromática sem a necessidade de uma cavidade. Ao longo dessa tese, detalhamos diversos estudos experimentais onde temos usado diversos corantes lasers da família das rodaminas em solução, às soluções temos adicionado nanopartículas de TiO2, tais nanopartículas realizam o papel de meio espalhador. O regime de espalhamento nesse sistema é difusivo pelo que a probabilidade do fóton confinado retornar ao ponto inicial de incidência é pouco provável, por tanto qualquer efeito de interferência das ondas associadas aos fótons podem ser negligenciadas. No capítulo 1 é feita uma apresentação rápida dos conceitos fundamentais sobre lasers e detalhando a física dos lasers de corante, logo falamos sobre o processo de espalhamento múltiplo de fótons. Iniciamos o capítulo 2 fazendo uma revisão histórica do laser aleatório com realimentação incoerente e discutimos alguns mecanismos que podem estar envolvidos no processo de geração de luz com características laser. No capítulo 4 apresentamos resultados de um estudo meticuloso sobre o limiar em lasers aleatórios considerando a influência tanto da densidade de espalhadores como da concentração de corante O capítulo 5 é dedicado ao estudo da influencia da agregação molecular e da emissão bicromática nas propriedades da emissão de um laser aleatório quando a concentração do meio de ganho é relativamente alta. No capítulo 6 apresentamos um novo método baseado na emissão de sistemas laser aleatório para determinar a energia de ligação entre moléculas individuais que se juntaram para formar agregados. Essa agregação sempre acontece entre as de moléculas de corante em solução, formando assim dímeros, trímeros, etc. Em primeira aproximação podemos falar de dimerização que é a formação de unicamente dímeros no processo global da agregação. Para descrever teoricamente essa nova técnica, utilizamos um modelo excitônico baseado na teoria quântica que explica como devido á dimerização a banda de absorção do monômero se desdobra em duas novas bandas: uma a altas energias (banda H) e outra a baixas energias (banda J). Os nossos resultados concordam muito bem com aqueles obtidos através de técnicas de absorção que são um tanto mais complicadas de se realizar experimentalmente. Usando nossa técnica determinamos a energia de ligação entre dímeros formados em diversos tipos de corantes da família das rodaminas. Finalmente, no capítulo 7 mostramos que possível se obter um laser aleatório com alta eficiência a partir de soluções aquosas contendo rodamina 6G. Nós adicionamos Dodecil Sulfato de Sódio (SDS, sigla em inglês), um surfactante aniônico, a uma solução de rodamina 6G (catiônica). Ambos os componentes foram preparados em diferentes concentrações. A ação do SDS sobre a rodamina 6G é inibir a agregação molecular e reorientar as moléculas agregadas remanescentes na solução a fim de formar agregados fluorescentes. Mostramos também que a eficiência deste tipo de sistemas atinge seu máximo para concentrações pouco acima da concentração micelar critica do SDS.

Orientador: Leandro Russovski Tessler / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-09T11:11:14Z (GMT). No. of bitstreams: 1 Bizuti_AriathemisMoreno_M.pdf: 8322758 bytes, checksum: 95ead73c1f59350e6aba71e4b5ca5ff4 (MD5) Previous issue date: 2005 / Resumo: Silício amorfo hidrogenado (a-Si:H) é um material amplamente usado na indústria microeletrônica. Ele é normalmente preparado a partir da decomposição do silano (SiH4). A diluição do silano em hidrogênio (H2) resulta em a-Si:H com propriedades eletrônicas superiores devido ao ataque químico preferencial às ligações mal-formadas. Níveis elevados de diluição resultam na formação de silício microcristalino (µc-Si). O objetivo deste trabalho é estudar o ordenamento da vizinhança química do silício através da transição a-Si:H ® µc-Si por espectroscopia de absorção de raios-X (XAS). Como a maior parte da desordem em a-Si:H manifesta-se na forma de variações nos ângulos de ligação, é necessário estudar o regime de espalhamento múltiplo (XANES), que corresponde às primeiras dezenas de energia (eV) acima da borda de absorção. Filmes finos de silício próximo à transição amorfo-microcristalino foram preparadas por HWCVD a partir de SiH4 diluido em H2. Nas condições utilizadas, a nucleação de µc-Si ocorre a partir de uma espessura crítica de aproximadamente 100 nm. Depositando-se amostras em forma de cunha é possível obter uma superfície de a-Si:H de um lado da amostra e de µc-Si do outro. Também foram investigadas amostras preparadas por PECVD em condições próximas à formação de pó no reator (chamadas de silício polimorfo, ou seja, entre amorfo e policristalino). Em princípio elas poderiam ter uma estrutura local mais ordenada / Abstract: Hydrogenated amorphous silicon (a-Si:H) is a material very used in the microelectronics industry. It is usually prepared starting from the decomposition of the silane (SiH4). Hydrogen dilution of the silane source gas is used to grow a-Si:H with superior electronics properties due to the preferential chemical attack to the bad formed bonding. High hydrogen levels induce the growth of microcrystalline silicon (µc-Si). The objective this work is study the order of the chemical neighborhood of the silicon through the transition a-Si:H ® µc-Si for x-ray-absorption Spectroscopy (XAS). As most of the disorder in the a-Si:H shows in the form of bonding angles variation, it is necessary to study the multiple scattering regime (XANES), that corresponds to the first dozens of energy (eV) above the absorption edge. Thin silicon films close the transition amorphous-microcrystalline was prepared for hot-wire chemical vapor deposition (HWCVD). For these conditions, the nucleation of the µc-Si oc-curs at a critical thickness of approximately 100 nm. Deposited the samples in the wedge form, it is possible to get a-Si:H surface in the one side and µc-Si in the other side. Also prepared samples were investigated for PECVD in close conditions to the powder formation in the reactor (calls of silicon polymorphous, a silicon sample between amorphous and polycrystalline) with the local order structure / Mestrado / Física da Matéria Condensada / Mestre em Física

Abstract Light scattering diagnostics of turbid media containing both structural and dynamic inhomogeneities is currently of significant importance. One of the important directions in modern light scattering diagnostics is the development of methods for probing biological media with visible- and near-infrared radiation allowing for visualization of the biotissue structure. Optical methods for studying the biotissue structure and characterization of its optical properties are very promising and have been rapidly developing during the past decade. The present work is aimed at improving and discovering new potentials of currently existing methods of laser diagnostics of biological tissues containing both structural and dynamic inhomogeneities. In particular, the feasibilities of spatially resolved reflectometry and time-of-flight techniques for the problem of noninvasive determination of glucose level in human blood and tissues were examined both numerically and experimentally. The relative sensitivities of these methods to changes in glucose level were estimated. Time-of-flight technique was found to be more sensitive. The possibilities of Doppler optical coherence tomography for imaging of dynamic inhomogeneities with high resolution were considered. This technique was applied for the first time for the imaging of complex autowave cellular motility and cytoplasm shuttle flow in the slime mold Physarum polycephalum. The effect of multiple scattering on the accuracy of the measured flow velocity profiles for the case of single flow and for the case of the flow embedded into the static medium with strong scattering was studied. It was shown that this effect causes significant distortion to the measured flow velocity profiles and it is necessary to take this into account while making quantitative measurements of flow velocities.

La coda ultrasonore présente une haute sensibilité aux perturbations du milieu de propagation. L'analyse de la coda par la Coda Wave Interferometry (CWI) permet d'évaluer précisément la variation de la vitesse de propagation (résolution en relatif de 0,001 %). Une telle évaluation peut être utilisée pour le contrôle non destructif (ECND) d’un matériau ou d'une structure.Un essai expérimental est présenté au début comme exemple d’utilisation de la CWI pour l’ECND du béton. Face aux problèmes inhérents au degré de précision de cet essai, nous présentons un protocole conçu pour améliorer la fiabilité des résultats CWI. Nous vérifions expérimenta vérifient que ce protocole peut améliorer la répétabilité de l’essai en réduisant les biais provenant des fluctuations de température ambiante et des procédures expérimentales. Avec ce protocole, une étude du comportement de béton sous un chargement uni-axial en traction directe a été effectuée en utilisant la CWI. Les comportements élastique (l’effet acoustoélastique) et anélastique (l’effet Kaiser) du béton sont observés via les résultats CWI. Un coefficient acoustoélastique effectif (Bêta) a été déterminé et utilisé pour la détection d’un endommagement léger du béton.La CWI est ensuite utilisée pour la détection globale de défauts dans un milieu initialement linéaire (verre) en observant la modulation non linéaire. L’apparition de ce phénomène non linéaire est due à la présence des défauts et détectée par la variation des résultats CWI en fonction de l’amplitude de l’onde de pompe. Nous montrons que cette méthode permet la détection des défauts et d’évaluation du niveau d’endommagement d’une manière globale sans zone aveugle. / With their long and complex propagation paths, coda waves can probe the propagation medium repeatedly and show a high sensitivity to the perturbations to the medium, i.e. variations in propagation velocity. Since such variations may indicate the modification of elastic properties and Coda Wave interferometry (CWI) can determine it precisely (relative resolution of 0.001%), CWI is considered a promising method for non destructive testing and evaluation (NDT&E). An experimental test is presented as an example of the CWI use on concrete for NDT&E purpose. For solving the experimental repeatability issue revealed in this test, a bias-control protocol is designed to reduce the experimental bias in CWI results. It is experimentally confirmed that this protocol can remarkably improve the reliability of CWI results and the experimental repeatability. Together with this bias-control protocol, the CWI is used to study the behaviors of concrete under uni-axial load in direct tension. Both elastic (acoustoealstic effect) and inelastic (Kaiser effect) behaviors are observed via CWI results. Effective value of acoustoelastic coefficient is then determined from CWI results and used for the detection of an early-stage damage that artificially induced to the concrete specimen. A defect-detection method of an initially linear medium (glass) is then developed by using the CWI. Due to the nonlinearity brought by the defects, acoustic mixing effect occurred, and the observation of such effect is the indication of damage. The use of a broadband pump wave and the CWI makes possible to 1) detect the damage globally without blind zone and 2) assess the damage level in an effective manner.

Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Liang-Wu Cai / A computational system is built for conducting deterministic simulations of three-dimensional multiple scattering of elastic waves by spherical inclusions. Based on expansion expression of elastic wave fields in terms of scalar and vector spherical harmonics, analytically exact solutions of single scattering and multiple scattering are obtained, implemented and verified. The verification is done by using continuities of displacement and surface traction at the interface between an inclusion and host medium, energy conservation and published results. The scatterer polymerization methodology is extended to three-dimensional multiple scattering solution. By using this methodology, an assemblage of actual scatterers can be treated as an abstract scatterer. This methodology is verified by using different approaches, with or without scatterer polymerization, to solve a physically the same multiple scattering problem. As an application example, band gap formation process for elastic wave propagation in cubic lattice arrangements of spherical scatterers is observed through a series of numerical simulations. Along the direction of the incident wave, scatterer arrangements are viewed as comprising layers of scatterers, within which scatterers form a square grid. Starting from one layer and by increasing the number of layers, near-field forward wave propagation spectra are computed as the number of layers increases. These simulations also demonstrates that the computational system has the capability to simulate multiple scattering solutions of elastic waves in three-dimension.

Ce travail de thèse est l'étude expérimentale de la propagation des ondes acoustiques dans un milieu granulaire sec et confiné. Ces ondes permettent de sonder de manière non invasive les propriétés viscoélastiques et la structure hétérogène du milieu, mais peuvent aussi être utilisées comme perturbation contrôlée pour étudier le réarrangement des réseaux des forces. Dans une première partie, nous nous intéressons à la propagation des ondes cohérentes dans les empilements des billes de verre et aussi dans ceux des grains irréguliers (sable). En régime linéaire, un très bon accord est retrouvé entre les vitesses d'onde de compression mesurées et celles prédites par la théorie des milieux effectifs, ce qui permet d'accéder au nombre de coordinance Z. En régime non linéaire, nous observons à la fois un softening et un hardening de la vitesse d'onde de compression à cause du changement de Z induit pat la forte vibration. La deuxième partie étudie la propagation des ondes multiplement diffusées. Nous montrons que le transport de ces ondes dans un milieu granulaire peut être décrit par le modèle de diffusion. Le coefficient de diffusion et l'absorption inélastique sont déterminés en fonction de la contrainte de confinement et de la fréquence d'onde incidente. Le libre parcours moyen versus la longueur d'onde relèvent deux régimes distincts du transport des ondes diffusées à basse et à haute fréquence. De plus, une décroissance non exponentielle est observée sur le profile d'intensité des ondes diffusées à temps long lorsque la fréquence de l'onde incidente devient importante. Une étude paramétrique basée sur la renormalisation du coefficient de diffusion est effectuée pour comprendre l'origine de ce transport diffusif anomal. Enfin, nous développons un dispositif (MRT) pour effectuer l'opération du retournement temporel dans un milieu granulaire. En régime linéaire, la recompression temporelle et la refocalisation spatiale sont vérifiées. Cependant, en régime non linéaire, nous observons que le processus du retournement temporel est brisé par l'interaction irréversible onde-matière, dû au changement ou réarrangement des réseaux des forces / This experimental work describes sound propagation in dry granular media. These sound waves provide a non invasive method to probe the viscoelastic properties and the heterogeneous structure of the materials. They may also be served as controlled perturbation to study the nonlinear response due to the rearrangements of the contact force networks. In the first part, we investigate the coherent wave propagation both in the packings of glass beads and those of irregular grains such as sands. In the linear regime, measured compressional wave velocities are in good agreement with the effective medium theory, giving access to the coordination umber Z. In the nonlinear regime, we observe both softening and hardening of the sound velocity, likely stemming from the change in Z caused by the strong vibration. In the second part, we study the multiple scattering of short-wavelength elastic waves in granular media. It is shown that the wave transport can be well described by the approximation of diffusion. We determine the diffusion constant and the inelastic absorption time as a function of the confining pressure and the frequency of the incident wave. The plot of the mean transport free path versus the wavelength shows two distinct regimes of transport in low- and high-frequency. Moreover, we find time-resolved intensity profile of multiply scattered waves exhibit a non exponential decay in long time, thus deviated from the classic diffusive transport. A parametric study using the renormalized diffusion constant is performed in order to understand the underlying physics of such anomaly wave transport. Finally, we perform a first experimental study of the time-reversal of ultrasound in glass bead packings. In the linear regime, we obtain by time-reversal processes both a temporal recompression and a spatial refocusing at the source transducer of an ultrasonic pulse transmitting through the disordered force networks. However, in the nonlinear regime, we observe a breakdown of the time-reversal of ultrasound due to the structural change of the materials, i.e. sound-induced rearrangement of the force networks

En présence de diffusions multiples, les algorithmes de Monte-Carlo sont trop coûteux pour être employés dans les algorithmes de reconstruction d'images de géométries tridimensionnelles réalistes. Pour des trajectoires de premiers retours, l'approximation de diffusion est communément employée afin de représenter la statistique des chemins aux nombres de Knudsen tendant vers zéro. En formulant des problèmes équivalents sur des trajectoires de premiers passages, l'usage de l'approximation est étendue en un développement théorique. Cette nouvelle formulation assure un bon niveau de précision, sur une large plage de valeurs du nombre de Knudsen en ce qui concerne l'évaluation des moments de la distribution des longueurs des chemins de premier retour. La résolution numérique du modèle formulé est confrontée aux simulations numériques type Monte- Carlo sur des géométries mono-dimensionnelles et un cas tridimensionel ouvrant des perspectives vers une généralisation aux applications réelles. / For multiple scattering, Monte-Carlo algorithms are computationally too demanding for use in image reconstruction of 3D realistic geometries. In the study of first return path, the diffusion approximation is commonly used to represent their statistical behaviour when the Knudsen number tends to zero. With the formulation of equivalent problems for first passage path, the use of the approximation is extended in a theoretical development. The new model provides a good level of accuracy, for a wide distribution of Knudsen numbers when evaluating the moments distribution of the first return paths length. Numerical application of the model is confronted to Monte-Carlo simulations on one dimension geometries and a simple three-dimension case opening perspectives for the generalization to practical applications.

O interesse na pesquisa de Lasers randômicos, meios dispersivos com alto ganho, tem crescido nos últimos anos em virtude das novas possibilidades advindas ao se trabalhar com estes sistemas, como emissões em bandas com baixo ganho, bicromaticidade, localização da luz em meios difusos e sistemas ópticos mais compactos. Nesse trabalho serão discutidos temas como espalhamento da luz por partículas, intensidade de retroespalhamento, ganho em meios desordenados e as transições energéticas do neodímio, correlacionando as emissões características obtidas nos experimentos com a teoria. Quanto aos resultados será apresentado a primeira observação de laser randômico com nanopó de Nd:YVO4 através de análise do comportamento da emissão espectral e temporal oriunda da transição 4F3/24I11/2 (1064 nm). Os resultados apresentam outra forma de analisar a cinética temporal da emissão de laser randômico, permitindo uma separação da fração de emissão estimulada e espontânea e comparação desse resultado com o estreitamento sutil da largura de linha, típico de lasers randômicos. As conversões ascendentes e saturação de ETU (conversão ascendente por transferência de energia) serão analisadas na mesma amostra, sendo todos os ajustes provenientes da literatura e de fundamental interesse, principalmente por se tratarem de um mecanismo de perda em lasers operando na região do infravermelho. Por fim, a emissão característica será avaliada pela técnica CBS (retroespalhamento coerente) para determinação da coerência do laser emitido e localização da luz neste meio difuso, com os resultados comparados aos da simulação. / In the past few years, the interest in random lasers, which refer to lasing in disordered media where strong multiple scattering plays a constructive role instead of being only a loss factor, have received considerable attention due to its unique properties and its potential applications, such as emission at new, extremely low gain lines, simultaneous emission of several very different wavelengths at the same time, strong light localization and miniaturization. Single and multiple particle light scattering, backscattering intensity, light diffusion with gain and the energy level diagram of Neodymium will be presented in this current work, alongside with a parallel from the typical emission lines obtained experimentally with theory. The demonstration of random laser action in Nd:YVO4 nanopowder, by analyzing the spectral and temporal behavior from the 4F3/24I11/2 (1064 nm) transition is presented. A method that analyzes the decay kinetics after long-pulse excitation is used to determine the laser characteristics, allowing measuring the fractional contribution of spontaneous and stimulated emission in the samples backscattering cone, with is in agreement to the smoothing linewidth narrowing as a function of pump power typical from random lasers. Also the visible emission along a method to determine quantitatively the ETU (energy-transfer upconversion) rate is presented, which is particularly interesting, as is a mechanism that introduces a loss channel for devices emitting in the infrared region. At last, the coherent laser emission and light localization will be evaluated by using the CBS (coherent backscattering) technique in this diffusive media, in which the results are compared with simulation.

Foi analisada, através de simulação Monte Carlo, a probabilidade de que um gap de rapidez seja observado na produção do boson de Higgs por fusão de bosons vetoriais com massa (W), no LHC (Large Hadron Collider). Foi analisada, também através do uso de Monte Carlo, a possibilidade de que a existência ou não de um gap de rapidez seja usada na distinção de um Higgs produzido por fusão de bosons vetoriais W de outro produzido por fusão de gluons. Os diferentes modelos para tratamento de processos não perturbativos dos códigos Monte Carlo DTUJET e PYTHIA foram comparados. / The gap survival probability for a higgs boson produced by W fusion at the LHC (Large Hadron Collider) is analyzed through Monte Carlo simulation. The possibility of distinguishing between two higgs production mechanisms, W and gluon fusion is studied using Monte Carlo simulation. The two different models for non pertubative processes, used by DTUJET and PYTHIA are compared.

Foi calculado microscopicamente a seção de choque total de reação para os sistemas ANTPOT. 12 C + ANTPOT. 12 C, ANTPOT. 1-2 C+ ANTPOT. 40 Ca, ANTPOT. 12 C + ANTPOT. 90 Zr, ANTPOT. 12 C + ANTPOT. 208 Pb, ANTPOT. 40 Ca + ANTPOT. 40 Ca, ANTPOT. 40 Ca + ANTPOT. 208 Pb, ANTPOT. 90 Zr + ANTPOT. 90 Zr, ANTPOT. 90 Zr + ANTPOT. 208 Pb e ANTPOT. 208 Pb + ANTPOT. 208 Pb numa ampla faixa de energia. Foi usada a expressão WKB para a defasagem imaginária, na representação do parâmetro do impacto. A parte imaginária do potencial óptico foi construída, usando o primeiro termo da teoria de espalhamento múltiplo, incorporando na sua expressão o principio de Pauli. A inclusão da interação nuclear e coulombiana mostrou ser importante. Os resultados teóricos não se apresentam em bom acordo com os poucos dados experimentais existentes, a baixas energias. Este resultado foi atribuído a fraca absorção contida no potencial imaginário, que contém o processo de knock-out quase-livre como mecanismo dominante de reação. / The total reaction cross section of the systems 12C +12C, 12C + 40Ca, 12C + 90Zr, 12C + 208 Pb, 40Ca + 40Ca, 40Ca + 208Pb, 90Zr + 90Zr, 90 Zr + 208 Pb and 20B Pb + 208 Pb for a wide range of energies has been calculated microscopically. A WKB expression for the imaginary part of the optical potential has been constructed by using the first term of multiple scattering theory with the effect of Pauli blocking incorporated into it. The inclusion of the nuclear and Coulomb interactions is shown to be important. The theoretical results do not show very good agreement with the experimental data at lower energies. This is attributed to the weak absorption contained in the imaginary potential of the tpApB interaction, wich contained only quasi-free knock-out as the dominant reaction mechanism.